Friday, April 4, 2014

`2, 9, 16, 23, 30, 37...` Decide whether the sequence can be represented perfectly by a linear or a quadratic model. If so, then find the model.

Firstly we need to determine whether the series is linear or quadratic. A linear sequence is a sequence of numbers in which there is a first difference between any consecutive terms is constant. However, a quadratic sequence is a sequence of numbers in which there is a second difference between any consecutive terms is constant. 


Now let's determine if the above sequence is linear or quadratic. 


Lets begin by finding the first difference: 


`T_2 -...

Firstly we need to determine whether the series is linear or quadratic. A linear sequence is a sequence of numbers in which there is a first difference between any consecutive terms is constant. However, a quadratic sequence is a sequence of numbers in which there is a second difference between any consecutive terms is constant. 


Now let's determine if the above sequence is linear or quadratic. 


Lets begin by finding the first difference: 


`T_2 - T_1 = 9 - 2 = 7`


`T_3 - T_2 = 16 - 9 = 7`


`T_4 - T_3 = 23 - 16 = 7`


From above we can see we have a constant number for the first difference, hence our sequence is linear.


Now let's determine the model of this sequence. The equation of a linear sequence is as follows: 


`T_n = a + d(n-1)`


Where 


T_n = Value of the term in sequence


a = first number of sequence


d = common difference (first difference)


n = term number 


Now let's substitute values into the above equation: 


`T_n = 2 + 7(n-1)`


`T_n = 2 + 7n - 7`


The model is simplified to: 


`T_n = 7n -5`



Now let's double check our model using terms 1, 3 and 6: 


`T_1 = 7(1) - 5 =2`


`T_3 = 7(3) - 5 = 16`


`T_7 = 7(6) - 5 = 37`


Summary: 


The sequence is linear. 


Model: 


`T_n = 7n - 5`



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